A mechanical health monitoring system for rotating machinery has to two primary objectives. One primary objective is issuing an advance warning of an impending failure. The other primary objective is preventing mission aborts and costly repairs due to primary and secondary damage. The advance warning period mentioned in the first objective can be extended by either detecting a spall early and with high confidence or by delaying the end of life as late as possible. The current practice is based on the manual inspection of an electronic chip detector and interpretation of the debris observed via human eye. The assessment of the mechanical health is based on the count of large particles and the frequency of such particles appearing over multiple inspections. The second objective demands that the end of life estimation should be highly accurate to avoid functional failure. The technical challenge is that while the incubation phase of a spall could last several tens of hours, the steady growth and rapid growth phases of a spall last in the order of hours and minutes respectively. The current practice for determining the end of life when utilizing an oil debris sensor is based on the accumulation of debris that covers the area between the two rolling elements on an inner race. The debris mass for such damage can be estimated, assuming that the fault is an inner race spall. However, the mass estimate is known to be only a rough order estimate. Also, the transition to rapid growth typically occurs roughly when the spall spans two rolling elements, but this is not precise, and can result in the end of life indication coming too close to functional failure. An indicator based solely on the debris mass could jeopardize the mission in cases where the fault does not progress like a typical inner race spall.
Therefore what is needed is automated continuous monitoring of the mechanical health of the rotating equipment to detect a spall as early as possible to allow enough time to schedule a repair and to detect the end of life with high confidence at the onset of a steady growth phase before it transitions in the rapid growth phase.